When is the best time to observe U Orionis?

U Orionis is best observed from November through January, with peak visibility during December when it transits around midnight in the Northern Hemisphere.

Where is U Orionis located in the sky?

U Orionis lies in the constellation Orion at right ascension 05h 56m and declination +20° 11′.

What telescope do I need to follow U Orionis?

To follow U Orionis through its full brightness cycle (magnitude 4.8 to 12.6) you need a telescope of roughly 190 mm or larger — the star fades out of smaller apertures near minimum light.

U Orionis — Variable Star in Orion

Observable Variable Star Showpiece (78/100)

Range: 4.80 - 13.00, Period: 371.7d, Type: M

Magnitude 4.8–12.6^m VariableStar Orion (Ori) Visible

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1Physical Properties

Magnitude 5.40

Range 4.80 - 13.00

Period 372 days

Variable Type Mira (Long-period Pulsating)

Spectral Type M6.5IIIe bright giant

Star Color Orange (B-V 0.99)

2Position & Identifiers

RA 05h 55m 49.3s

Dec +20° 10' 30.0"

Constellation Orion (Ori)

HR 2063

HD 39816

SAO 77730

Variable ID U Ori

3How easy to follow?

Magnitude 4.8 – 12.6 mag Amplitude 7.8 mag Period 371.7 d Type M

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Equipment	Bortle 3	Bortle 4	Bortle 5
Naked eye Naked eye	Imp.	Imp.	Imp.
50 mm finder 50mm finder	Imp.	Imp.	Imp.
150 mm telescope 150mm scope	Hard+	Hard	V. hard+

Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

To reach "Medium" at Bortle 3, you'd need at least a 190 mm reflector.

4Visibility

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Best season Nov – Jan (peak: Dec)

5Survey Image

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6Light Curve

7Comparison Stars for U Ori (4.8–12.6)

Nearby stable stars for estimating brightness (AAVSO)

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8

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9

Spectral Classification

10

Hertzsprung-Russell Diagram

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Read: The Hertzsprung-Russell Diagram — Reading Stars Like a Map

11

Stellar Lifecycle

12

Blackbody Spectrum

13

Stellar Absorption Spectrum

Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.

14

Stellar Fusion

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15Stellar Notes

Variable Star

M 4.8 - 12.6v, 368.3d. Period has varied between 367.9 and 376.0d. Colors correspond to 6.72V.

Spectral

Infrared star. OH and water emission. SiO maser source. OH emission strong in infrared. Also H2O microwave | emission. IR spectra show water vapor. Strong water bands at light minimum.

Remarks

Occultation diam. = 0.0143 - 0.01545".